The present invention relates to a signal encoding and decoding circuit for a television (hereinafter, referred to as TV) receiver and transmitter, and more particularly to a circuit which changes the input signal by changing the state of assigning address to a memory.
In a generally adopted TV a transmission and reception method, image, voice and other various synchronizing signals from a video camera are modulated and transmitted via transmission antenna, and the original image and voice signals are restored in a receiver set by demodulating the transmitted signals. Recently, only the restricted viewers with cables are allowed to receive the broadcast by using a cable method instead of a wireless method, and a cable TV transmission and reception method is introduced for improving an image quality. Recently, however, since a transmitting part transmits a scrambled transmission signal in order to charge service fee for transmitted data, a transmission and reception method requiring for a device decoding the transmitted signal is introduced into a receiving part, in the wireless and cable TV transmission and reception methods. In the next generation for the TV transmission and reception method, the stated above method is to be used for the purpose of reducing noise. The above method for scrambling (encoding) the signal was used for military purposes in the early stage, but recently it is frequently being used in TV or satellite communications as stated forgoing.
FIG. 1 is a conventional circuit for scrambling the signal, and it is illustrated hereinafter.
First, a scrambler 50 for scrambling a signal in a receiving part is described. A key-data generator 102 controlled by a controller 101 generates regular serial data composed of a given number of bits. A first pseudo-random address generator 103 supplied with the data output from the key-data generator 102 addresses a memory 104 pseudo-randomly when input signal is stored in the memory. When the stored data is read out from the memory 104, the input signal is randomly mixed with the stored data, by sequentially addressing the memory in response to mode signal output from a controller 101 and by reading out the data randomly stored in the memory 104 . In this case, reading out and writing operation is determined by read and write signal output from the controller 101. Since the regular data output from the key-data generator 102 is inserted between the data output from output terminal D0 of the memory 104 while the data output from the memory 104 passing through a key-data inserting unit 105, the input signal 1 is completely scrambled.
Next, an unscrambler 60 for unscrambling the scrambled signal output from the above scrambler 50 is described. The scrambled signal output from the key-data inserting unit 105 is transmitted through a cable or a wireless transmission and applied to a card reader and key-data separator 107. When a user enters selected data onto a magnetic card 108 in order to restore the scrambled signal to the original signal, the card reader and key-data separator 107 compares the above selected data with the key-data, if equal to, applies data to a memory 110 after erasing the key-data. At the same time, the card reader and key-data separator 107 addresses the memory 110 opposite to that of address generator 103 which is pseudo-randomly addressed by a second pseudo-random address generator 109 in order to store the input signal 1 randomly in the memory 104 of the scrambler 50. Accordingly, the scrambled signal from the scrambler can be restored in the memory 104. A controller 106 generates control signals in order to operate the card reader and key-data separator 107 and the second pseudo-random address generator 109 as stated above, and applies read/write signal to the memory 110.
The conventional scrambler circuit 50 and unscrambler 60 circuit in FIG. 1 described above have disadvantages of being very complex and requiring very high technology. Furthermore, when the above circuits are implemented on TV, it becomes a factor for higher cost of TV units.